The present invention relates to a pump unit and a method for evacuating drying spaces wherein vacuum drying of aqueous and other solvents-containing laboratory specimens is carried out.
Certain research, testing and like procedures involve vacuum drying specimen compositions which include or are embodied in a solvent vehicle. Solvents used generally can include water, acids, organic liquids, etc. Frequently, the compositions will be as gels.
Evacuation of the space in which drying is carried out, commonly is effected with, e.g., a diaphragm pump which can be a single stage or a plural pumping stage type unit. The attendant reduction of space pressure to values well below atmospheric pressure as well as application of heat to the drying space and/or specimen, causes the solvents present to be drawn from the specimen in liquid form and also to evaporate from the specimen, both such solvent forms being drawn out of the evacuation chamber along with chamber headspace gases. The vapors of some of these solvents are readily condensable when pressure values are increased in the diaphragm pump unit which must compress the gas flow outdraw from the drying space so it can be discharged to atmosphere or subjected to a recovery processing. Liquid solvent "slugs" if drawn into the pump, can damage it and to a degree requiring replacement or rebuilding of the pump.
Where diaphragm pump units have been used in the past for this purpose, the prior art has sought to ameliorate the potential for liquid solvent presence and vapor condensation in the pump by employing, e.g., cold traps to condense liquid vapors before the gas flow enters the pump unit. But pre-trap cooling is expensive both as to initial equipment and operating cost because very low order cooling temperatures must be maintained. Also, Bell jars have been used as pre-traps, but these Bell jars have the disadvantage that they can implode under vacuum and possibly injure workers nearby. More importantly though, is that these prior used pre-traps require periodic cleaning to remove trapped solvent. To effect this cleaning, the vacuum lines must be broken, i.e., disconnected. Over a period of time this can effect integrity of the lines, but of more immediate disadvantage is that if cleaning needs be done in the middle of a drying cycle, the system vacuum level must be reestablished prolonging the overall drying period and expending energy unnecessarily. Further, prior pump unit/pre-trap arrangements allowed for solvent to condense and collect, inter alia, in hose loops and in pump inlets and outlets as well. Such condensed solvent represents a stagnant liquid mass that simply sits obstructively in the system and retards the drying action, it being especially an acute problem where the condensed solvent is in a hose loop. The hose functions as an insulator and blocks out any form of heat entry to the solvent that could vaporize same.